Andrés Manuel López Obrador, president of the left-leaning National Regeneration Movement, center, arrives for an event on Sunday in Los Angeles. The politician known as AMLO is the early front-runner in Mexico’s 2018 presidential race. (Dania Maxwell/Bloomberg News)

LOS ANGELES — Abel Flores, a 45-year-old day laborer, left central Mexico three decades ago and has not voted regularly in its elections. And yet, as the sun was setting on a recent evening, he was jammed with hundreds of Mexican Americans into a tree-shaded Los Angeles plaza to cheer on a rabble-rousing politician who could take Mexico in a very different direction.

“I don’t normally do this kind of thing,” Flores said, referring to the rally for Andrés Manuel López Obrador, widely known as AMLO. But the day laborer felt that Mexico was threatened by President Trump, who has vowed to build a border wall and renegotiate the historic free-trade agreement with the United States.

“AMLO is the only person who can do anything to protect Mexico,” Flores declared.

The outrage in Mexico over Trump’s proposals has elevated a longtime politician who has unnerved the country’s business community with his nationalist views and leftist rhetoric. Political opponents have compared López Obrador with the late Hugo Chávez, a strongman who steered Venezuela toward socialism. While that may be an exaggeration, López Obrador, 63, can bring thousands into the streets on command. His critics worry that his penchant for stubborn resistance could provoke confrontation with the United States, while his fans see him as a defender of the common man.

Although he has not yet officially declared his candidacy for next year’s presidential race, López Obrador has become the clear front-runner: A recent poll by El Financiero newspaper had him capturing 33 percent of voter support, six points ahead of Margarita Zavala of the conservative National Action Party (PAN). López Obrador is already in campaign mode, barnstorming the country and traveling to the United States to drum up support from Mexican Americans.

As he spoke to the crowd in Plaza Olvera in Los Angeles on Sunday, López Obrador hit some fiery notes, comparing Trump’s America to Hitler’s Germany, but he ultimately called for calm.

“We should counter the strategy of Trump and his advisers not with shouts and insults . . . but with intelligence, wisdom and dignity,” he said. “This is a battle that we should wage on the terrain of ideas.”

Trump will probably be a major campaign issue when Mexicans go to the polls next year. López Obrador has criticized the U.S. president’s policies but showed restraint, casting himself as the mature elder statesman. On the night Trump won the election, López Obrador posted a short video telling Mexicans that they had “no reason to worry” and that they belonged to a sovereign nation that “doesn’t depend on any foreign government.” During the current standoff with Trump over who will pay for the border wall, López Obrador has refrained from bashing President Enrique Peña Nieto, who is accused by some Mexicans of being too accommodating.

A fixture on Mexico’s left for decades, López Obrador comes from the gulf coast state of Tabasco, where he ran unsuccessfully for governor. He gained prominence as the mayor of Mexico City from 2000 to 2005, cutting an unusual figure by avoiding many of the trappings of high office and driving around in a Nissan Sentra. He gave subsidies to the poor and elderly but also balanced the budget, built elevated roadways to relieve the city’s notorious traffic, and raised tax collection. He left office with an approval rating of more than 80 percent.

But in 2006, after narrowly ­losing the presidential election, ­López Obrador provoked a political crisis by refusing to accept the victory of Felipe Calderón, a conservative, and instead declaring himself the nation’s “legitimate president.” The leftist showed his mastery at mobilizing crowds, leading a six-week blockade of one of Mexico’s main boulevards.

After he again lost the presidential election in 2012, López Obrador left Mexico’s main leftist party — the Party of the Democratic Revolution (PRD) — and formed an offshoot called MORENA, or the National Regeneration Movement.

Peña Nieto and his traditionally dominant Institutional Revolutionary Party (PRI) have become deeply unpopular because of a sluggish economy, corruption scandals and the perception that the president has not stood up to Trump. Peña Nieto and his team have been careful not to antagonize Trump, for fear of damaging the relationship with Mexico’s No. 1 trade partner.

“Andrés Manuel is well positioned in this situation to create an alternative path, and he has benefited a lot because Peña Nieto’s team has been clumsy,” said Alberto Aziz Nassif, a political analyst in Mexico City. “He is reading these new winds, these new times.”

López Obrador has been a front-runner before only to fade as the election gets closer. His criticssee him as an arrogant, power-hungry figure. Much of the business and political elite consider him a particular threat. He has been skeptical of Mexico’s embrace of free trade and opposed Peña Nieto’s moves to open the country’s crucial oil industry to foreign investment.

“He is authoritarian, intolerant, he has a vision of the world where those who are with him are good and the others are bad,” said Francisco Gil Villegas, a political analyst in Mexico City. “He’s not very democratic, and he is willing to operate above the Constitution.”

Despite his long political history, López Obrador sees himself as an outsider. In a speech on Sunday at a cultural center in ­Tijuana, south of the border from San Diego, he warned that the electoral system was rigged, and he predicted fraud in next year’s vote.

His new book, “2018 The Exit: Decline and Rebirth in Mexico,” opens with the line: “Corruption is the principal problem in Mexico,” a theme he has emphasized since his first presidential run a decade ago.

In his Tijuana speech, López Obrador estimated that hundreds of millions of dollars in government funds are siphoned away each year in corruption and promised that he would recover this money — he did not specify how — and spend it on scholarships for students. He vowed to sell all the presidential airplanes and helicopters and travel in a more humble fashion. These types of promises resonate with many Mexicans who are fed up with rampant corruption.

The crowd that greeted López Obrador in Los Angeles later that day included documented and undocumented immigrants, migrant advocates and Dodgers first baseman Adrián González, who is Mexican American. Trump’s threats to deport illegal immigrants and the recent wave of immigration raids in several U.S. cities have alarmed many in the Mexican diaspora.

Los Angeles was the first of seven U.S. cities that López Obrador plans to visit in coming weeks as he casts himself as a defender of immigrant rights. At the end of his Tijuana speech, he led a chant that immigrants “are not alone.”

In his remarks, López Obrador was deeply critical of Trump, ­describing him as a “neo-fascist” who won the presidency through a “discourse of hate.” But he called for opposing the U.S. president through legal and democratic means. He urged bilingual lawyers to help migrants and suggested that media outlets document the migrant experience.

“I confess that I am optimistic,” he said. “The wall and demagoguery can’t compete with the talent and dignity of the United States.”